State-of-the-art circuit interrupters such as described within U.S. Pat. No. 4,672,501 entitled "Circuit Breaker and Protective Relay Unit" employ digital circuitry to perform overcurrent protection along with supplementary electronic function. To provide electronic input to the circuit interrupters from associated electrical equipment, transducers such as current transformers and Hall effect devices, such as described in U.S. Pat. No. 5,615,075 entitled "AC/DC Current Sensor for a Circuit Breaker" are often required.
The current transformers usually provide two functions within the electronic trip unit circuit. The first function is to provide operating power to the electronics within the trip unit and the second function is to provide electronic signals representative of the magnitude of the current flowing within each phase of a multi-phase electrical distribution system. U.S. Pat. No. 5,583,732 entitled "Modular Current Transformer for Electronic Circuit Interrupters" describes a recent approach to combine the two functions within a single modular arrangement.
Since the current sensing and power-up transformers are usually contained within the circuit breaker enclosure, along with the circuit breaker operating mechanism, contacts and trip unit, the space requirements are governed by the size of the transformers. When four and five pole circuit breakers are required as within European and Asian distribution circuits, the size of the circuit breakers are increased accordingly.
It would be beneficial to be able to provide a minimum size current transformer for power-up function while using small-sized electronic transducers for determining the current magnitude in view of cost and size restraints with multi-pole circuit breaker applications.
One purpose of the invention accordingly, is to provide a multi-pole circuit breaker having the smallest conceivable power-up transformers and current sensors.